1. Field of the Invention
The invention is directed to denture adhesive liners and to methods of making and using such liners.
2. Description of Related Art
Dentures and dental plates function as a substitute for all or part of missing teeth ordinarily found in the mouth. While dentures are usually carefully fitted for the user, the fit can change over time, causing discomfort and slippage. To alleviate the discomfort and to control the slippage, a denture adhesive may be applied to the denture.
Denture adhesives typically contain a material that forms a gasket between the denture and the gum line. Generally, the gasket-forming material is a water swellable gum or polymer. The gum or polymer hydrates and becomes tacky when introduced to the saliva in the oral cavity, thus holding the dentures in place.
The constant flow of saliva in the oral cavity, however, can cause premature washing away of the gum or polymer, so oils and petrolatum are also used in a denture adhesive to suspend the gum or polymer and so delay the washing away. The effective life of the gum or polymer during use is thereby increased.
Denture adhesives are usually applied as a cream or paste to the dentures before wearing. These highly viscous materials may be unpleasant to work with and may not provide an even hold at all points in the denture. Pressure gradients may cause the denture adhesive to migrate away from areas where the gum or other oral tissue is uncomfortably close to the denture material, thus reducing any cushioning effect of the adhesive at precisely the point where it is most needed. Migration of the denture adhesive material can also adversely affect the gasket that is formed by the adhesive between the denture and gums, thereby reducing the holding ability of the adhesive.
One alternative to traditional denture adhesives is a denture liner. A denture liner is a fixed, usually self supporting, layer coated with at least one layer of an adhesive material.
The self supporting layers used in past denture liners do not generally assist in the adhesive function. Rather, the self supporting layer holds the adhesive in place to limit or prevent migration of the adhesive, allowing an effective gasket to remain at the site selected by the user. Self supporting layers used in the art include plastic films, non woven fabrics, woven fabrics, and paper. Each of these materials can provide mechanical strength to support denture adhesive liner products and may prevent or reduce migration of the denture adhesive away from problem areas. But, these self supporting layer materials do little to enhance the strength of the gasket formed by the self supporting layer and the associated adhesive. In addition, these self supporting layers tend not to have the necessary flexibility and conformablilty required for fully comfortable denture adhesive products. The more inflexible the liner, of course, the greater the chance that the adhesives on the liner will fail to bond well to the irregular surfaces of the dentures and oral tissues. The gasket formed by the adhesive is correspondingly weaker, and may fail entirely.
A very early denture adhesive liner patent, U.S. Pat. No. 1,917,902 to Rowe, issued Jul. 11, 1933, describes a gum tragacanth adhesive on a cotton gauze self supporting layer. While cotton gauze is an acceptable material from a technical standpoint, the appearance of a product made in accordance with Rowe may have reduced its appeal in commercial use.
A commercial denture liner marketed under the name SEA BOND is described in U.S. Pat. No. 4,503,116 to Lapidus, issued Mar. 5, 1985. This liner uses a two-layer self supporting layer. The layers are bound together with a thermoplastic mixture of a polyethylene oxide and sodium alginate.
Another commercial product, marketed under the name TOUCH CORRECT, is discussed in U.S. Pat. No. 4,880,702 to Homan et al., issued Nov. 14, 1989. The patent discloses the use of adhesive outer layers containing an adhesive made from either a mix of polyethylene oxide and carboxymethyl cellulose or polyvinyl alcohol. The adhesive is held in place during use with a self supporting layer comprising microcrystalline wax, polyethylene oxide and carboxymethyl cellulose.
U.S. Pat. No. 5,158,825 to Altwirth, issued Oct. 27, 1992, is directed to a nonwoven fabric impregnated with a mixture of polyvinyl acetate and sodium alginate or carboxymethyl cellulose. This product is also on the market under the name FITTYDENT or SECURE.
U.S. Pat. No. 5,6568,586 to Rajaiah et al. (Rajaiah I) and European Patent Application No. 788,341 to Rajaiah et al. (Rajaiah II) are directed to compositions that may contain up to 70% of one or more therapeutic agents which are suitable for mucosal or topical administration. The patent describes a wide range of well known denture adhesive polymers, including salts of GANTREZ acid, Karaya gum, carboxymethyl cellulose, sodium alginate, and polyethylene oxide, but it specifically excludes polyvinyl acetate as a suitable adhesive component.
Rajaiah I calls for applying a weak pressure sensitive adhesive ("PSA"), polybutene, to one side of the liner product and then applying an aqueous solution of a partial GANTREZ salt adhesive to the other side to bond the liner to the dry denture adhesive material.
One recently published PCT application, WO 97US11,720 to Rajaiah et al., filed Jul. 3, 1997 and claiming priority from U.S. patent application Ser. No. 08/677,713, filed Jul. 8, 1996 (Rajaiah III), is directed to the use of a zinc Gantrez salt with a denture liner. The self supporting layer material may include polyester or polypropylene or nylon, nonwoven fabrics or fleece, paper, plastic, leather, microcrystalline wax, synthetic fibers, natural fibers and mixtures thereof.
Despite the progress that has been made in the use of denture liners, the search for more effective materials continues. There is still a strong need in the art for a liner that is both strong enough to withstand use in the oral environment and conformable enough to provide a well adhered gasket in use.